In the field of bar code reading, there is increasing use of mobile readers used in roaming mode, as opposed to readers directly connected to a fixed data processing system, for example to a point of sale terminal. Roaming devices pose a number of problems.
One problem is battery capacity, and it is desirable to reduce power consumption to alleviate this. Typically the reader will be placed in a standby mode when not actively reading. When a reading is then taken, it is necessary to set the exposure level in accordance with ambient conditions; and, in prior art systems this is commonly done by taking a significant number (e.g. typically about 20) of frames of differing exposures and then selecting the best exposure for the ambient conditions. However, this number of frames leads to unnecessary power consumption and can cause problems due to movement of the reader during the process.
Another problem with roaming devices is that they are used in greatly differing ambient conditions which may range from direct sunlight to very low illumination levels within warehouses. Many designs have a default configuration in which the target is illuminated by LEDs, which consume a great deal of power. It would be desirable to disable the LEDs as quickly as possible where ambient illumination is sufficient to permit this. The above problems become even more pronounced with reading 2D symbols rather than 1D bar codes.